Household waste water from homes and industrial waste water from offices are collected through sewage work to waste water treatment facilities where the waste water is purified through various treatment processes and then is discharged to rivers and/or seas.
On the other hand, various deodorizers are used to suppress diffusion of offensive smell from sewage collected at the waste water treatment facilities.
FIG. 1 illustrates an example of a waste water treatment system or facility where an ozone deodorizer as disclosed in Japanese Utility Model 3002318 is applied. This waste water treatment system comprises an upwardly opened treatment vessel body 1, a cover 2 on the vessel body 1 and an exhaust pipe 4 vertically extending through the cover 2 and having an exhaust fan 3 at its intermediate portion.
The treatment vessel body 1 is buried in the ground in such manner that the cover 2 is positioned near the ground surface. Provided inside the vessel body 1 are pre-treatment, adjustment and aeration vessels 5, 6 and 7.
Sewage to be treated flows from outside into the pre-treatment vessel 5 via a screen 8 which serves to remove relatively large dust and refuse.
The sewage treated in the pre-treatment vessel 5 flows over a weir between the vessels 5 and 6 into the adjustment vessel 6 since new sewage flows from outside into the vessel 5. Likewise, the sewage treated in the adjustment vessel 6 flows over a weir between the vessels 6 and 7 into the aeration vessel 7 since new sewage flows from the pre-treatment vessel 5 into the adjustment vessel 6.
Further, the sewage, which has been purified by the various treatment processes in the vessels 5, 6 and 7 to have BOD (biochemical oxygen demand) and the like values within levels as allowable by laws, regulations and the like, is pumped from the aeration vessel 7 by a pump (not shown) and is discharged to rivers and/or seas.
The ozone deodorizer comprises a filter box 9 for removing particulates and the like in the air through filtration of the air, an oxygen generator 10 for extracting oxygen (O.sub.2) by applying and reducing pressure on the air filtered through the filter box 9, an ozone generator 11 for generating ozone (O.sub.3) by applying high voltage on the oxygen from the oxygen generator 10, a fan 12 for sucking and discharging the air, a discharge pipe 13 extending through the cover 2 such that its upstream and downstream portions are positioned above and below the cover 2, respectively, and a plurality of branch pipes 15 connected to the downstream portions of the discharge pipe 13 and communicated with a space 14 defined by the cover 2 and the treatment vessel body 1.
The above-mentioned filter box 9, oxygen generator 10, ozone generator 11 and fan 12 are arranged outside the treatment vessel body 1. An ozone outlet of the ozone generator 11 and an air outlet of the fan 12 are connected to the upstream portion of the discharge pipe 13.
In the waste water treatment system shown in FIG. 1, actuation of the oxygen generator 10, ozone generator 11, and fan 12 causes mixture of ozone generated by the ozone generator 11 with the air from the fan 12 to flow through the discharge pipe 13 and branch pipes 15 into the space 14 defined by the cover 2 and vessel body 1.
The ozone contained in this mixture oxidizes smell components such as hydrogen sulfide (H.sub.2 S) and ammonia (NH.sub.3) emitted from the sewage to be treated in the vessels 5, 6 and 7 to reduce the offensive smell.
However, half-life of ozone in the atmospheric air is about 13 hours. As is disclosed in the above, reaction rate of oxidation of the smell components emitted from the sewage inside the waste water treatment system is not very high. Relatively long time is required for the reaction of ammonia with ozone so that the reaction may be carried out inefficiently within the limited time.
From these reasons, in the waste water treatment system shown in FIG. 1, the offensive smell components emitted from the sewage may not be sufficiently oxidized by ozone and may be discharged together with unreacted ozone to outside through the exhaust pipe 4, resulting in diffusion of the offensive smell outside the waste water treatment system.
Also a deodorization method has been proposed in which ozone and water are mixedly sprayed through atomizer nozzles so as to generate hydroxyl radicals (OH radicals), which have higher activity than ozone and may be used for oxidization of smell components. However, pressure of ozone flow from ozone generating means such as the ozone generator 11 is less than 1 kg/cm.sup.2 and water cannot be sprayed out through the atomizer nozzles only by the ozone flow from the ozone generating means. As a result, no hydroxyl radicals are generated.
To solve the above problems, it is an object of the present invention to ensure spraying pressure at atomizer nozzles for mixedly spraying ozone and water and efficiently remove smell components.